Adjust rack to top position and preheat oven to 425 degrees. Wash and dry all produce. Trim and thinly slice scallions, separating whites from greens. Heat a drizzle of oil in a small pot over medium-high heat. Add scallion whites; cook 1-2 minutes. Stir in rice and 3/4 cup water (11/2 cups for 4 servings). Bring to a boil, then cover and reduce heat to low. Cook until tender, about 15 minutes.

Meanwhile, drain pineapple over a small bowl, reserving juice. Roughly chop pineapple. Trim green beans. Zest and quarter lime. In a second small bowl, combine pineapple, scallion greens, lime zest (to taste), juice from 1 lime wedge, and 2 TBSP pineapple juice (3 TBSP for 4 servings). Season with salt and pepper.

Toss green beans on a baking sheet with a drizzle of oil, salt, and pepper. Roast on top rack until browned and tender, 10-12 minutes.

Pat barramundi dry with paper towels; season all over with salt and pepper. Season flesh side of fish with Southwest Spice; rub to evenly coat.

Heat a large drizzle of oil in a large pan over medium-high heat. Add barramundi, skin side down. Cook until skin is crispy, 4-5 minutes. (TIP: Lower heat if skin begins to brown too quickly.) Flip and cook until fish is cooked through, 2-3 minutes. Turn off heat; transfer to a paper-towel-lined plate.

Fluff rice with a fork; stir in 1 TBSP butter (2 TBSP for 4 servings), remaining lime zest (to taste), and juice from 1 lime wedge. Season with salt and pepper. Divide rice, barramundi, and green beans between plates. Top fish with salsa. Serve with remaining lime wedges on the side for squeezing over.