Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Wash and dry all produce. Dice sweet potatoes into 1/2-inch pieces. Core, deseed, and dice poblano into 1/2-inch pieces. Halve, peel, and cut onion into 1/2-inch-thick wedges; mince one wedge until you have 1 tsp (2 tsp for 4).

Toss sweet potatoes, poblano, and onion wedges on a baking sheet with a large drizzle of olive oil, half the cumin (you’ll use more later), salt, and pepper. (For 4 servings, divide veggies between 2 baking sheets; roast on top and middle racks.) Roast on top rack until lightly browned and tender, 20-25 minutes.

Meanwhile, finely dice tomato. Zest and quarter lime (for 4 servings, zest 1 lime and quarter both). Mince cilantro. Mince or grate 1 clove garlic (2 cloves for 4). Thinly slice jalapeño into rounds; mince a few slices until you have 1/2 tsp (1 tsp for 4). TIP: Remove ribs and seeds from jalapeño for less heat.

In a small bowl, combine sour cream, cilantro, minced onion, juice from half the lime, a pinch of minced garlic, a pinch of minced jalapeño, a small pinch of cumin (you’ll use the rest later), and 1 TBSP olive oil (2 TBSP for 4 servings). Taste and add more garlic if desired. Add water 1 tsp at a time until mixture reaches a drizzling consistency. Season with salt and pepper.

Pat barramundi dry with paper towels and season all over with salt and pepper. Season flesh sides with remaining cumin; rub to evenly coat. Heat a large drizzle of oil in a large, preferably nonstick, pan over mediumhigh heat. Add barramundi skin sides down. Cook until skin is slightly crisp, 4-5 minutes. Flip and cook until barramundi is opaque and cooked through, 2-3 minutes more.

Toss roasted veggies with tomato and lime zest; divide between bowls or plates. Place barramundi on top. Drizzle with creamy salsa verde and top with sliced jalapeño if desired. Serve with any remaining lime wedges on the side.