Can I see an overview of my settlers?

No, unfortunately there is no overview of what all of your settlers are doing. However you can see what each individual is assigned to if you have visibility of that individual and their assigned task - this picture will show you what I mean:

This settler is only assigned to half of these carrots, another settler is doing the others, so when I target this settler is highlights half of the carrots.

There is, however, an overview of all of your settlements available in your Pip Boy, under the Data > Workshops tab:

This will warn you of any issues at each of your settlements.

As of 11/11/2015 there is no settler interface.

The beta patch for 1.3 released on Jan 15th does show settler assignments when you hover over the settler. A wonderful and much needed improvement.

As the accepted answer states, the Vault-Tec Population Management System added by the Vault-Tec Workshop DLC was an attempt to add this feature. The system is, however, fairly limited. It works for basic task tracking, and provides a quest that can track companion locations. It does not, however, work with robot settlers built via the Robot Workbench, nor does it work with robot companions such as Codsworth or Ada.

If you are on PC, there is a mod available called "Settlement Management Software" by matzman666. The mod is essentially a more robust version of the Vault-Tec Population Management System and works with robot settlers. It also reflects renamed settlers, showing the new name instead of just "Settler". According to the mod's description page, it provides the following features:

• List additional stats to your settlement
• Manage any settlement from any terminal
• See details for every single settler.
• Mark unassigned/individual settlers, provisioners and attack spawn markers with quest markers so that you find them more easily
• Move settlers to a different settlement
• Assign settler to an unused workshop object
• Assign settler to a supply route
• Identify those pesky synths among your settlers (Requires enabled Cheat option)
• List all workshop objects in a settlement
• List all workshop objects assigned to a settler
• Mark unassigned workshop objects
• Reset supply lines from/to a settlement

Note that I am not associated with the mod or its author, nor have I even used it myself yet (although I intend to). I've simply seen it used in various mod review videos, and it seems to do what you're asking about. I realize the original question is five years old, but perhaps this will help someone else as well.

Unfortunately no, there is no current settler interface within fallout 4. Like mentioned by kalina, you can see the tasks in build mode by hovering to the settler in question. To make it easier to find their tasks (especially in big places like the castle), use the tfc 1 console command (assuming you're on pc) to hover around the settlement to check if the settler indeed has an assigned work.

To make things a lot easier, you can give them certain "uniform" to know what they're working. My guards have the sack hoods, my scavengers have the gas assault mask, my provisioners have minutemen outfits, etc.