Drain the diced tomatoes. In a medium bowl, combine the drained tomatoes with the olive oil, lemon juice, minced garlic, oregano, salt, and pepper. Stir well, then set the tomato mixture aside. Preheat the oven to 400ºF.

Place the chicken breasts on a cutting board and cover them with a sheet of plastic wrap. Use a mallet or rolling pin to carefully pound the chicken breasts to an even thickness. Don't pound with too much force or the breasts may split. Start at the thickest part of the breast and work your way out toward the edges. Once pounded, slice each chicken breast into two portions and season each side with a pinch of salt and pepper.

Drain the can of artichoke hearts and roughly chop them into smaller, bite-sized pieces. Place a handful of the artichoke pieces in the bottom of a casserole dish, then lay the chicken pieces over top. Cover the chicken with the remaining artichoke pieces and the bell pepper. Pour the tomato mixture over top.

Bake the chicken, uncovered, in the fully preheated oven for 30 minutes. After 30 minutes, sprinkle one cup of mozzarella over top. Switch oven's setting from bake to broil and broil the dish (on the middle rack) for about 5 minutes or until the cheese is bubbly and browned. Serve immediately.