Place clams in saucepan. Pour in water and add lemon juice. Cover and cook 5 minutes, stirring once during cooking. Remove saucepan from heat. All clam shells should be fully opened. Discard unopened clams. Let clams stand in cooking liquid to keep warm.
Heat oil in sautee pan over medium heat. Add shallots, garlic and green onions. Mix and cook 4 minutes over low heat.
Add red pepper and tomatoes. Season, add tarragon and cook 12 minutes over medium heat.
Place linguine on plates. Arrange clams still in their shells on pasta. Ladle sauce over and serve.