Preheat the oven to 400°F (200°C). Line a sheet pan with parchment paper and set aside.

Peel the beet, potatoes, carrots, and red onion. Discard onion outer skin after peeling.

Cut the vegetables: slice the beet; cut the potatoes into wedges; cut the carrots into pieces roughly the same thickness as the beet slices; quarter the red onion; cut the broccoli into larger florets; core and seed the red bell pepper, then cut it into squares.

Place 6 oz pesto in a large bowl. If the pesto is too thick to coat the vegetables, stir in up to 2 Tbsp olive oil until it reaches a coating consistency.

Add all prepared vegetables to the bowl with the pesto and toss until every piece is evenly coated.

Spread the coated vegetables in a single layer on the prepared sheet pan. Sprinkle evenly with 1/2 tsp salt and 1/4 tsp black pepper and toss gently on the pan to distribute the seasoning.

Roast in the preheated oven for 30–35 minutes, stirring or flipping the vegetables once about halfway through. Begin checking doneness and browning at 20–25 minutes.

If you want more charred color, switch the oven to broil for the last 5 minutes—move the pan to the upper oven rack and watch closely to prevent burning. Remove from oven and let rest a few minutes before serving.