Roast the vegetables: Preheat the oven to 425°F (220°C).Cut 2 pounds cherry tomatoes in half and arrange them cut side up on a large rimmed sheet pan. Add 1 medium onion cut into wedges and 1 whole garlic head (top trimmed off). Drizzle with 3 tablespoons extra virgin olive oil, season with 1½ teaspoons dried oregano, 1 teaspoon salt, ¼ teaspoon red pepper flakes, and black pepper, then turn the garlic cut side down.Roast for 30 to 40 minutes, until the tomatoes are soft and blistered and the onions are tender.
Cook the orzo: About 10 minutes before the vegetables are done, cook 1 cup orzo in salted boiling water until al dente, following the package directions. Drain well.
Toss everything together: Squeeze the soft roasted garlic cloves onto the sheet pan and mash them with a fork.Add the hot orzo, 1 cup crumbled feta, ⅓ cup basil leaves, and the grated zest of ½ lemon. Toss everything together right on the sheet pan so the orzo soaks up all the tomato juices.
Serve: Taste and add more salt and pepper if needed. Serve warm with extra basil, feta, black pepper, or a drizzle of olive oil if you like.
Substitutions
Cherry tomatoes → Grape tomatoes, date tomatoes, or chopped ripe Roma tomatoes.
Onion → Red onion, sweet onion, shallots, or white onion.
Garlic → Omit it, or use extra onion plus garlic-infused olive oil.
Dried oregano → Italian seasoning, dried thyme, or dried basil.