Heat oven to 425 degrees. Spray 18×13-inch rimmed sheet pan with non-stick cooking spray. Spread out sliced fennel, sweet onion, garlic, carrots, potatoes and sliced lemon in one layer on the sheet pan. Drizzle with 1-2 tablespoons of olive oil and season with minced rosemary, salt and pepper. Squeeze the juice of half of a lemon over vegetables. Toss vegetables with hands to combine and spread out evenly on the sheet pan.