Preheat oven to 400.
Cut the cherry tomatoes in half and dress with the garlic, sliced onion, olive oil, rosemary, lemon zest and coriander seed.
Lay out skin side up on a parchment lined baking sheet. Roast until tomatoes begin to brown and blister- about 20 minutes.
Remove from the oven and transfer the blistered tomatoes to a bowl. Season with the balsamic vinegar, red pepper flakes, sea salt and black pepper.
Serve warm or at room temperature.