Preheat oven to 425°F and line a sheet pan with aluminum foil for easy cleanup.
In a small bowl, combine lemon juice, lemon zest, 2 tablespoons olive oil, thyme, rosemary, minced garlic, salt, and pepper to create a marinade.
Pat chicken thighs dry and rub the lemon herb mixture all over them, making sure to get some under the skin for maximum flavor.
Toss bell peppers and red onion wedges with remaining 1 tablespoon olive oil, salt, and pepper.
Arrange chicken thighs skin-side up on the sheet pan and scatter vegetables around them, then tuck lemon slices among the vegetables.
Roast for 35-40 minutes until chicken reaches an internal temperature of 165°F and skin is crispy and golden brown.
Let rest for 5 minutes before serving, squeezing the roasted lemon slices over everything for extra brightness.