Preheat your oven to 400°F (200°C).

In a large mixing bowl, combine olive oil, lemon juice, Dijon mustard, oregano, thyme, red pepper flakes, smoked paprika, salt, and pepper. Whisk until smooth.

Add chicken thighs, chopped red bell pepper, sliced yellow onion, Kalamata olives, and minced garlic to the marinade. Toss to coat.

Transfer the mixture to a greased baking dish, spreading it in an even layer.

Bake for 25-35 minutes until the chicken reaches an internal temperature of 165°F (74°C) and vegetables are fork-tender.

Let it rest for a few minutes before serving.