Steps
1. In a bowl, mix brewed coffee, soy sauce, brown sugar, and minced garlic to create the marinade.
2. Add beef strips to the marinade and let sit for 15 minutes.
3. Heat oil in a pan over medium-high heat.
4. Add sliced onions and bell peppers; stir-fry until slightly softened.
5. Remove vegetables and set aside.
6. Add marinated beef to the pan and stir-fry until cooked through, about 4-5 minutes.
7. Return vegetables to the pan, mix well, and cook for another 2 minutes.
8. Season with salt and pepper to taste.
9. Serve hot, optionally with cooked rice.