Preheat oven to 400°F.
Mix beef with salt and pepper and shape into 4 patties. (If you wish to make smaller burgers, feel free to make more patties, seal off extras in a freezer bag, and save as a back-up plan for another week).
Spray a foil lined baking sheet with cooking spray. Place patties onto pan and bake for 5-6 minutes. While baking, dice peppers and onion.
Flip burgers over and sprinkle them all with some peppers and onions. Bake an additional 6-12 minutes or until no longer pink in the centers. You may also want to pull out the meat thermometer, making sure it reads at least 160°.
While baking, cut tomato into thin slices.
Add burgers to buns, topping each with a slice of tomato and lettuce. Serve with grapes on the side.