Preheat oven to 350. Line a rimmed baking sheet with nonstick foil.
Toss the potatoes, shallots and tomatoes with the olive oil and vinegar and place in a single layer on the baking pan. Bake until the vegetables are tender and roasted, about 20 minutes.
While the vegetables are roasting, sauté the spinach in a large skillet until wilted and set aside.
Whisk the eggs with a pinch each of salt and pepper.
When the vegetables are done, leave the oven on and transfer them to a deep dish pie plate or similar baking dish that you have sprayed with nonstick spray. Add the spinach and spread the veggies out evenly.
Pour the egg mixture on top and bake for 30 minutes. Let cool for a few minutes and then cut and serve, drizzling a little olive oil on top and grinding on some fresh pepper if you like!
Notes
Sweet Potato: These orange root veggies are sometimes displayed in the supermarket as yams, although they are actually not the same thing (yams are much larger and starchier than sweet potatoes).
Plum Tomatoes: Look for these oval tomatoes in your produce section. While you can swap them out for round tomatoes, plum tomatoes give the richest flavor when you roast them.
Spinach: You can swap out large leaf spinach for baby spinach if you like – just give it a good chop before you cook it so it is bite-sized in your frittata.
Shallots: Look for these members of the onion family in your produce section.