Smoked Fish Crostini

Name: Smoked Fish Crostini
Ingredients: 1 cup cherry tomatoes, halved or quartered; 7 tablespoons olive oil, divided; 2 teaspoons fresh lemon juice; 4 large green or purple basil leaves, thinly sliced, plus small leaves for garnish; Kosher salt and freshly ground black pepper; 1 bunch spring onions or scallions, trimmed; 8 1/4'-thick slices country-style rye bread; 8 ounces fresh farmer cheese (about 1 cup), fromage blanc, or cream cheese; 8 ounces smoked fish, preferably sablefish, deboned, flaked into 1' pieces (about 1 3/4 cups) or thinly sliced if using salmon; 1 /2 cup thinly sliced assorted cucumbers (such as kirby and Persian)