Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Wash and dry produce.

Cut potatoes into ½-inch pieces and place in a small pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 10-12 minutes; drain.

Transfer potatoes to a medium bowl. Add crème fraîche, salt, and pepper; toss to combine. Taste and season with more salt and pepper if desired.

While potatoes cook, trim green beans if necessary. Dice tomato into ¼-inch pieces. Pick and roughly chop fronds from dill. Peel and mince or grate garlic.

Toss green beans on one side of a lightly oiled baking sheet with a drizzle of oil, salt, and pepper (spread out across entire sheet for 4 servings).

Pat tilapia* dry with paper towels and season generously with salt and pepper; place on empty side of same sheet. (For 4, use a second baking sheet.)

Roast on top rack until green beans are browned and tender and tilapia is cooked through, 10-12 minutes. (For 4, roast on top and middle racks, swapping rack positions halfway through.)

In a small bowl, combine tomato, dill, garlic, vinegar, and 1½ TBSP olive oil (3 TBSP for 4 servings). Season with salt and pepper.

Transfer a splash of liquid from tomato-dill relish to bowl with potato salad; toss to combine.

Divide potato salad, green beans, and tilapia between plates. Spoon relish over tilapia and serve.