In a mixing bowl, whisk together the olive oil, ground cumin, chili powder, garlic powder, salt, and freshly cracked pepper. Add the chicken breasts to the bowl, ensuring they are evenly coated with the marinade. Allow the chicken to sit at room temperature for at least 15 minutes to absorb the flavors.
Preheat a grill pan or a skillet over medium-high heat. Once hot, place the marinated chicken breasts in the pan. Cook for about 6-7 minutes on each side, or until the chicken is fully cooked and the juices run clear when pierced. After cooking, transfer the chicken to a cutting board and let it rest for about 5 minutes before slicing it into thin strips.
Using the same skillet, add the sliced red bell pepper and onion. Sauté the vegetables over medium heat for approximately 3-4 minutes or until they become tender yet still retain a slight crunch. Season with salt and freshly cracked pepper to enhance the flavors.
Warm the corn tortillas in a dry skillet over medium heat for about 30 seconds on each side until they become soft and pliable. Stack them on a plate, covered with a clean cloth to stay warm.
On each warmed tortilla, layer a generous amount of sautéed bell peppers and onions, followed by the sliced chicken and succulent diced mango.
Sprinkle fresh cilantro leaves on top of each taco for a burst of flavor and color. Serve the tacos with lime wedges on the side, to squeeze over the top just before enjoying.