Make salsa: Arrange a rack in the highest part of the oven. Then, preheat the broiler. Place poblano and jalapeño on a baking sheet. Toss onion slices with 2 teaspoons oil to lightly coat and add to baking sheet with peppers. Broil, carefully turning peppers and tossing onion slices with tongs every 2 minutes. Remove onion when tender and charred in spots (about 3 to 4 minutes), then remove peppers when blackened all over (about 5 to 7 minutes). Place peppers in a bowl, cover, and let steam for 10 minutes. Mince onion and place in a separate medium bowl.
Once peppers are still warm but cool enough to handle, remove skin, halve, and remove seeds. Then, mince peppers and add to bowl with onion. Fold in strawberries, lime juice, and cilantro. Season with salt and pepper.
Make fish: Preheat oven to 400 degrees F. Season fish all over with salt and pepper. Pour ¼ cup oil into a 9-by-13-inch baking dish and scatter garlic slices throughout. Add fish, turn to coat in oil, and roast until opaque and flakes with a fork, 12 to 15 minutes. Baste with oil, then serve with salsa on top.