Slice chicken, beef, shrimp, or vegetables into thin strips
Season with chili powder, cumin, garlic powder, paprika, salt, and pepper
Heat oil in a skillet over medium-high heat
Cook the protein until browned and cooked through
Remove the protein from the skillet
Add sliced onions and bell peppers to the skillet
Cook until softened and lightly charred
Return the protein to the skillet
Add a squeeze of lime juice and toss everything together
Warm tortillas in a pan or microwave
Serve the fajita filling with tortillas
Add toppings such as salsa, guacamole, sour cream, cheese, or cilantro