Preheat oven to 350°.
To prepare tomatoes, coat a foil-lined baking sheet with cooking spray. Place tomatoes, cut sides up, on baking sheet. Drizzle with 1 tablespoon oil; sprinkle with 1/2 teaspoon salt, 1/2 teaspoon thyme, 1/2 teaspoon pepper, and garlic. Bake at 350° for 1 1/2 hours or until very soft and slightly shriveled, turning occasionally.
To prepare risotto, bring broth to a simmer in a medium saucepan (do not boil). Keep warm over low heat.
Heat 1 tablespoon oil in a large saucepan over medium-high heat. Add leek; sauté 3 minutes or until tender. Add rice; cook 1 1/2 minutes, stirring constantly. Stir in wine; cook 30 seconds or until liquid is nearly absorbed. Stir in 1 cup broth; cook 3 minutes or until liquid is nearly absorbed, stirring frequently.
Add remaining broth, 1/2 cup at a time, stirring frequently until each portion of broth is absorbed before adding the next (about 25 minutes). Stir in arugula, half-and-half, cheese, 1/4 teaspoon salt, and 1/4 teaspoon pepper.
To prepare salmon, heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Sprinkle salmon with 1/2 teaspoon salt, 1/2 teaspoon thyme, and 1/4 teaspoon pepper. Place fillets, skin sides up, in pan; cook 5 minutes. Turn fillets over, and cook an additional 2 minutes or until fish flakes easily when tested with a fork.
Arrange 3 tomato halves, cut sides up, in a spoke-like pattern in center of each of 6 plates. Mound 2/3 cup risotto in center of each plate (leaving about a 1 1/2-inch edge of tomatoes uncovered). Arrange fillets on risotto. Garnish with thyme sprigs, if desired.