In a food processor, whirl garlic to mince. Add red tomatoes, 1 1/2 cups yellow tomatoes, the bell pepper, 1/2 cup oil, the lime zest, 5 tbsp. lime juice, white parts of green onions, the chile, 1 1/2 tsp. salt, and the pepper; whirl until almost smooth.
Transfer to a bowl, stir in shrimp and crab, and chill, covered, at least 2 hours.
Cut remaining yellow tomatoes in half. Stir most of avocado into soup and season to taste with more lime juice and salt. Divide soup among bowls and top with yellow tomatoes, remaining avocado, and green parts of green onions. Drizzle with olive oil.
Make ahead: Through step 2, up to 1 day, chilled.