Heat the olive oil in a pan. Add the ground beef. Cook until no longer pink, stirring to break up any lumps. Add the chilis and bell pepper. Season lightly with salt and pepper. Cover and cook over medium heat for about 15 minutes. Place a strainer over a bowl, pour the beef mixture into the strainer and allow the fat to drip off. Cool.
When the beef has cooled, stir in the mozzarella cheese and half of the cheddar cheese.
Dip both sides of an tortilla in the tomato sauce. Lay flat on a plate and place a heaping tablespoonful of the filling at the center. Roll and place on a baking pan, seam side down (for a visual guide, please refer to the chicken enchiladas recipe).
Repeat until all the filling has been used up or until you run out of tortillas, whichever comes first. In my case, I was able to fill 18 tortillas.
Divide the remaining tomato sauce among the baking pans and pour over the tortillas. Top with the remaining shredded cheddar cheese. Bake in a preheated 425F oven for 10 to 15 minutes or until the cheese melts and the tomato sauce is bubbly.
Use a wide spatula to lift the enchiladas and transfer them to individual dinner plates.