Tomato & Goat Cheese Gratin

Preheat the oven to 450 degrees. Place sliced onion and pepper (if using) in a microwave-safe bowl and toss with 2 tablespoons olive oil, a pinch of salt and thyme sprigs. Cover with plastic wrap and microwave until the onions soften, about 2½ minutes. Remove from the microwave and let the bowl rest, covered, until slightly cooled.
Uncover bowl and discard thyme. Spread onion mixture across the bottom of a medium baking dish or ovenproof pan. With a spoon, scoop and discard the seeds and pulp from tomatoes. Season the interiors with salt and pepper and place tomatoes over the onions, cut side up, in a snug single layer.
Scatter the tomatoes with half the basil, then top with an even layer of crumbled goat cheese. Top with the breadcrumbs, Parmesan and remaining olive oil.
Bake until the tomatoes are soft and the goat cheese bubbles and browns in spots, about 20 minutes. Remove the gratin from oven, let rest at least 5 minutes, then top with remaining basil leaves and a drizzle of olive oil. Serve immediately, with bread for dipping, if desired.​

1 small onion, thinly sliced
1 poblano pepper, halved, seeded and thinly sliced (optional)
⅓ cup olive oil plus extra for drizzling
Kosher salt and freshly ground black pepper
6 sprigs fresh thyme
3 pounds small tomatoes, halved crosswise
6 tablespoons basil leaves, roughly torn
6 ounces fresh goat cheese, broken into large crumbs
⅓ cup breadcrumbs
⅓ cup Parmesan cheese
Crusty bread (optional)​