In a bowl, whisk together olive oil, lemon juice, minced garlic, oregano, paprika, salt, pepper, and red pepper flakes. Add chicken and coat well. Cover and marinate in the refrigerator for 15-45 minutes.

Chop cucumbers, tomatoes, bell pepper, and red onion. Combine with parsley and feta cheese in a mixing bowl. Season with salt and pepper, and mix until combined. Let sit for flavors to meld.

Preheat a skillet over medium-high heat. Add the marinated chicken and cook 3-5 minutes per side until golden brown and cooked through. Remove from heat and let rest before slicing.

Warm pitas over a gas flame for about 30 seconds each side or in a skillet for about 1 minute. Alternatively, wrap in foil and warm in the oven at 350°F for 5 minutes.

Assemble the tacos by filling each warm pita with chicken slices, vibrant salsa, and tzatziki sauce. Serve immediately and enjoy!