Preheat oven to 425 degrees F. Place potatoes in a large bowl. Drizzle with 1 Tbsp. of the oil and sprinkle with coarsely chopped garlic and 1/8 tsp. of the salt and black pepper; toss to coat. Transfer to a 15x10-inch baking pan; cover with foil. Roast 30 minutes.
Meanwhile, thaw salmon, if frozen. Combine, in the same bowl, sweet peppers, tomatoes, chopped parsley, pitted halved olives, finely snipped oregano and 1/8 tsp. of the salt and black pepper. Drizzle with remaining 1 Tbsp. oil; toss to coat.
Rinse salmon; pat dry. Sprinkle with remaining 1/4 tsp. salt and black pepper. Spoon sweet pepper mixture over halved lengthwise potatoes and top with salmon. Roast, uncovered, 10 minutes more or just until salmon flakes.
Remove zest from lemon. Squeeze juice from lemon over salmon and vegetables. Sprinkle with zest.
Percentages are based on a diet of 2000 calories a day.