Make the mojo de ajo: Cook oil and garlic in a small saucepan over low heat until garlic is soft and fragrant, about 8 minutes. Remove from heat, and stir in lime juice, red-pepper flakes, and salt.
Make the fajitas: Heat a large skillet (preferably cast-iron) over high heat. Add oil, and gently swirl to coat. Add onion and bell pepper, and season with 1/4 teaspoon salt. Cook, stirring frequently, until onion is browned in spots, and pepper has softened slightly and skin is blistered, about 5 minutes. Add chicken and 1 teaspoon salt, and cook, stirring frequently, until chicken is browned and cooked through, 5 to 7 minutes. Add the mojo de ajo, and stir to coat. Season with salt and pepper. Serve immediately with warmed tortillas, guacamole, pico de gallo, sour cream, and cheese.
Warming a Tortilla: There is more than one way to warm a tortilla. For a charred version, turn a gas burner to high. Using tongs, heat a tortilla directly over the flame, flipping it often, until dark spots form on both sides. Another stove-top technique is to set a tortilla in a dry skillet and warm it over medium-high heat for about 10 seconds, turning the tortilla once. You can also use a microwave: Simply place a tortilla between damp paper towels, and heat in microwave for 30 seconds.