Scrub the shellfish clean. Heat 2 tablespoons of the olive oil in a heavy pot over medium heat. Place the clams and mussels in the pot and cover. The shells should be open in about 7 to 10 minutes. (discard any that don't) Strain and reserve the liquid. Remove the shellfish from the shells and discard the shells. Dice the shrimp, clams, and mussels.
Chop 1 clove of the garlic and saute in the remaining tablespoon of oil in a skillet over medium heat; do not let it brown. Add the shellfish, parsley, and pepper flakes. Cook for 2 minutes. In a separate pot, combine the tomatoes, wine, and reserved shellfish broth over medium heat. Cook for 3 to 4 minutes, until thickened. Add to the shellfish and cook for 2 more minutes. Remove from the heat.
Rub the bread with the remaining 2 garlic cloves and brush with olive oil. Arrange in a single layer on a sheet pan and toast both sides. Top each piece of toast with a portion of the seafood mixture, arrange on a platter and serve warm