Preheat the oven to 400 degrees and line 1-2 large baking sheets with parchment paper.
Make the marinade. Add olive oil, lemon juice, red wine vinegar, garlic powder, dried oregano, marjoram, red pepper flakes, salt, and pepper in a small bowl or jar. Whisk to combine.
Marinate the chicken. Add chicken thighs to a bowl or plastic bag and toss with half of the marinade. Let marinate while you prep the remaining ingredients. You can also put it in the fridge and let it marinate for 30 minutes to 8 hours.
Chop and mix the veggies. While the chicken quickly marinates, cut your potatoes, onion, and bell peppers and add to your large baking sheet. Pour over the remaining marinade and mix until the veggies are fully coated. Spread out evenly on the pan.
Add chicken thighs. Nestle your chicken thighs in your veggies on the baking sheet, spreading them out evenly. Make sure all veggies are spread out on the pan and not piled on top of each other as the juice released from the chicken gives them more flavor and helps them cook evenly. If needed, move some chicken and vegetables to another baking sheet.
Bake. Roast for 35 minutes. Add tomatoes, olives, and feta, spreading them out evenly on the pan, and bake for another 5-15 more minutes until veggies are tender and chicken is cooked through. If desired, place under the broiler and broil for a couple of minutes to get everything a little more crispy.
Enjoy! I like serving over some chopped romaine with some tzatziki sauce, lemon juice, and fresh dill.