In a bowl, whisk together olive oil, lemon juice, minced garlic, oregano, and salt and pepper. Add chicken breasts and let marinate in the fridge.

While the chicken marinates, grate cucumber and squeeze out excess moisture. Mix with Greek yogurt, minced garlic, lemon juice, dill, and salt. Refrigerate.

Heat a skillet over medium-high heat and cook marinated chicken breasts for 6-8 minutes per side until golden brown. Remove from heat and let rest before slicing.

As the chicken cooks, prepare toppings: halve cherry tomatoes, slice red onion, crumble feta cheese, and prepare spinach or arugula.

Warm tortillas in a dry skillet or microwave until soft and pliable.

Spread tzatziki on a tortilla, layer with sliced chicken, cherry tomatoes, red onion, feta, and greens. Drizzle more tzatziki if desired.