Pat the chicken breast dry and season both sides with salt, pepper, and half of the dried oregano; rest for 5 minutes.

Heat olive oil in a skillet over medium-high heat. Sear chicken for 5-6 minutes until golden, then flip and cook for another 3-4 minutes.

In the same skillet, add more olive oil. Sauté garlic for 30 seconds, then add red bell pepper and yellow squash; cook for 4-5 minutes.

Add cherry tomatoes and cook for 2 minutes. Return the chicken to the pan with spinach, remaining oregano, and red pepper flakes; stir and cook for 2-3 minutes.

Remove from heat, zest a lemon on top, adjust seasoning, and serve hot, optionally over rice or couscous.