Preheat your oven to 400°F (200°C).

In a large skillet, heat olive oil over medium heat. Add ground beef and taco seasoning, cooking for 5-7 minutes until fully cooked. Add diced onions and bell peppers.

Place taco shells upright in a baking dish. Spoon the filling into each shell and top with shredded cheese.

Bake in the preheated oven for 10-12 minutes until the cheese is bubbling and golden.

Garnish with shredded lettuce, diced tomatoes, jalapeños, and sour cream before serving.