Preheat oven to 325°F. Drain tuna and place oil in a small bowl. Place baguette slices on a baking sheet and brush with oil on both sides. Sprinkle lightly with salt and pepper. Bake until crisp and golden, about 10 minutes. Remove from heat and let cool. Place tuna in a small bowl. Add lemon juice, tomatoes, garlic and half the basil, stirring to combine. Season with salt and pepper. Place tuna mixture on toast and garnish with remaining basil before serving.