Preheat oven to 400 degrees F. Peel and cube sweet potato, cut brussels sprouts in half, and chop pepper and leek. Toss everything with 2 tablespoons of olive oil and ½ teaspoon kosher salt and half of the black pepper.
Spread out veggies on a lightly oiled sheet pan.
Nestle two large chicken breasts in the veggies. Drizzle with extra oil and season the chicken well with extra seasoned salt, kosher salt, and pepper on both sides. Also add in garlic cloves and rosemary for aromatics.
Bake sheet pan for 30-35 minutes until chicken is cooked through and reaches 165 degrees F. in the thickest part and the veggies are soft and blistered in parts. You don’t need to stir the veggies during baking. Just let them go.