In a large skillet over medium heat, brown 1 pound of ground beef, breaking it apart with a spatula, for about 6-8 minutes until no longer pink. Drain any excess fat.

Add 1 chopped onion and 1 cup of diced bell peppers to the skillet. Sauté for 3-5 minutes until the onion turns translucent and the peppers soften.

Stir in 2 cups of Mexican cheese blend and sprinkle over taco seasoning to taste. Cook for about 2-3 minutes.

Lay out thick slices of bread and spread the beef and cheese mixture onto half of the slices. If desired, add sliced avocado.

Heat a skillet or panini press over medium heat. Grill the sandwiches for about 3-4 minutes on each side until golden brown.

Remove sandwiches from the skillet and let them cool for about a minute. Slice each sandwich in half and serve hot, alongside Mango Slaw.