In a small bowl, combine the chili powder, cumin and red pepper flakes.
In a large skillet or saute pan, heat the olive oil and minced garlic on medium heat.
Toss the pepper and onions in the pan with the garlic and saute for 3 to 5 minutes, then add half of the seasonings and saute another 3 minutes. Remove the sauteed peppers and onions from the pan and set aside on a plate.
To the same skillet, add the steak strips and remaining seasoning and saute for 8 to 10 minutes, or until cooked through. Toss in the peppers and onions back into the pan and saute together another 3 minutes.
Remove from heat and spoon steak, peppers and onions onto flour tortillas. Garnish with sour cream, salsa and shredded cheese.
Serve Steak Fajitas with favorite garnishes, if you're really feeling festive, with rice and beans for side dishes!