The ingredients in a fajita will work perfectly well in a frittata. Season and cook as if making a fajita and you have a fajita frittata.
A few notes: The meat and vegetables in a fajita are traditionally made and served in strips. For a frittata, I think it makes sense to cut these strips into shorter pieces. For the bell peppers, I would choose to use red and yellow peppers in a fajita for maximum contrast. (Green pepper would not be my choice for a fajita.) But for the frittata, with the eggs being yellow, I chose an orange pepper to have contrast with the eggs. And of course the frittata ingredients can be prepared however you like to make fajitas. The chicken is often marinaded, and everyone seems to use a slightly different mixture of spices.
Chicken fajita frittata
4 ounces, 1/2 cup chicken breast, cut into strips and then shorter pieces
1/3 cup red bell pepper cut into strips and then into shorter pieces
1/3 cup orange or yellow bell pepper cut into strips and then into shorter pieces
1/3 cup red or yellow onion, sliced and cut into pieces
1/4 teaspoon chili powder
1/4 teaspoon ground cumin
1/8 teaspoon paprika
1/8 teaspoon oregano
fresh ground pepper
Mix the spices. Heat oil in a pan over moderately high heat. Add the chicken and sprinkle on over half of the spice mixture. Cook, turning frequently until chicken is browned and cooked through, 3 to 4 minutes. (These are small pieces, so they will cook quickly.) Remove the chicken from the pan and add the vegetables and a bit more oil if needed. Sprinkle on the remaining spice mixture. Turn down the heat to medium and cook until the vegetables are soft, 4 to 5 minutes. Remove from pan. Depending on the amount of the spices remaining in the pan, you may want to wipe it out before proceeding with the frittata.
Put the eggs into a good-sized mixing bowl and beat just to mix them up. Add a bit of oil to the pan and let it get hot. Add a small amount of the eggs to the pan to set the bottom of the frittata to prevent sticking. Turn the heat down to medium low. Mix the chicken and vegetables into the eggs. Pour the mixture into the pan. Cook this for about 5 minutes to set the bottom and sides.
Preheat the broiler. When the 5 minutes cooking on the stove are up, place the pan under the broiler, about 6 to 7 inches below. Cook until the top is set and just starts to brown. This is about 1–1/2 to 2 minutes for me, but watch closely.
Remove from the broiler, loosen up the sides with a spatula if necessary, and slide the frittata out onto the serving plate. Serve with pico de gallo or salsa.