Heat a skillet or saute pan over medium-high heat. Add first part of oil and then chicken. Cook in batches until cooked through, 3 to 4 minutes on each side. Transfer chicken to a cutting board and return pan to the burner.
To the hot pan, add the second part of oil and then onions, bell peppers, zucchini and garlic. Saute until tender, ~4 minutes. Add spinach and saute just until spinach is wilted, ~2 minutes more. Season with some salt and pepper.
Slice chicken and serve over spinach and vegetables. Enjoy!