Peel onions and cut each through stem ends into halves (do not remove stem ends; they help to hold onion halves together). In 4-quart saucepan bring water to a boil; add onions. Reduce heat and let simmer until onions are tender, 10 to 12 minutes. Drain well. Scoop pulp from each onion half, leav-ing about a 1/2-inch-thick shell; reserve shells. Chop enough pulp to measure 1 cup; transfer chopped pulp to medium mixing bowl and add broccoli, Parmesan, mayonnaise, and lemon juice. Mix well and set aside. In 10-inch skillet heat margarine until bubbly and hot; add flour and salt and stir quickly. Stirring, gradually add milk; bring just to a boil, Reduce heat and let simmer, stirring frequently, until smooth and thickened; add Monterey Jack and cook, stirring constantly, until melted. Preheat oven to 3750F. Fill shells with onion mixture and set in 8 x 8 x 2-inch bak-ing dish. Top with sauce; sprinkle with paprika. Bake until sauce is bubbly, about 15 minutes. MAKES 6 SERVINGS, 1/2 ONION EACH Each serving provides: 1 Protein Exchange: 2 vegetable Exchanges: 1 1/2 Fat Exchanges: 1/4 Milk Exchange: Per serving: 242 calories; 14 g protein; 14 g fat; 17 g carbohydrate: 431 mg calcium.. 523 mg sodium; 28 mg cholesterol Kathy Dionne Coceur d?Alene, Idaho Posted to recipelu-digest by Ron West on Feb 28, 1998