Mix up the marinade by combining salsa verde, olive oil, lime juice, brown sugar, garlic, cumin, salt and pepper.
Whisk together.
Mix with the sliced steak.
Pour the mixture into a zip top bag and seal, removing any air. Refrigerate 1 - 4 hours.
Prepare a grill fire to 400°. Heat a griddle or grill pan until sizzling hot.
Pour the steak with marinade onto the griddle. Add the peppers and onions, stirring to combine.
Cook with the grill closed, stirring every 5 minutes.
Continue to cook until steak is seared and vegetables are softened. We cooked ours for about 15 minutes.
Remove to a serving platter.
Warm tortillas on the grill.
Serve fajitas with tortillas, sour cream, guacamole, tomatoes, cheese and cilantro.