1. Preheat oven to 400°.
2. Toss 1 1/2 teaspoons olive oil, 1/8 teaspoon salt, and tomatoes on a parchment-lined jelly-roll pan. Bake at 400° for 15 minutes or until tomatoes burst.
3. Heat 3 1/4 cups water and broth in a saucepan over medium heat (do not boil).
4. Heat remaining 1 1/2 teaspoons oil in a large Dutch oven over medium-high heat. Add onion to pan; cook 5 minutes, stirring frequently. Add rice; cook 1 minute. Stir in vinegar; cook 30 seconds or until the liquid is absorbed, stirring constantly. Add broth mixture, 1/2 cup at a time, stirring constantly until each portion is absorbed before adding the next (about 20 minutes total). Add peas and asparagus to pan with last 1/2 cup of broth mixture. Remove from heat; grate 1 ounce cheese. Stir in grated cheese, remaining 3/8 teaspoon salt, and juice. Spoon about 1 3/4 cups risotto into each of 4 bowls; top evenly with tomatoes. Shave remaining cheese evenly over each serving; sprinkle with pepper.