In a large skillet, sauté onion, garlic, green pepper, red pepper and jalapeno until softened, about 5 minutes. Add diced tomatoes and optional can of tomato sauce, stirring to combine. Add shredded chicken, chili and cumin powder and mix well. Simmer for 10 minutes. Add salt and stir to combine. Set aside.
To Make Beef Filling
In a large skillet, sauté onion and garlic for 3-4 minutes or until soft. Add ground beef, breaking up into small pieces. When beef is cooked, add green pepper, red pepper, jalapeno, chili and cumin powder and mix well. Add diced tomatoes and optional can of tomato sauce, stirring to combine. Simmer for 10 minutes. Add salt, stir and set aside.
To Make Tacos
In a large skillet, heat vegetable oil. Have a tray or plate with paper towels ready for tortillas to drain. Test oil by putting a small piece of tortilla in the oil. If bubbles, it's ready to fry. Place corn tortillas, one at a time, into the oil. Fry on each side for about 10 seconds. Remove to paper towel and fold tortilla in half. Repeat process with the remaining tortillas. Fill each tortilla with 2 heaping tablespoons of chicken or beef filling. Sprinkle with 2 teaspoons of cheese. Seal tacos with toothpick and return tacos to the skillet that you fried the tortillas, cooking in batches if necessary. (You may have to add more oil to the pan (3-4 tablespoons total) so the tacos don't stick to the pan.) On medium high heat, cook tacos until slightly crisp of both sides, turning once during cooking process. When done, place tacos on platter, added shredded lettuce, more cheese if desired, chopped tomatoes or pico de gallo.