Prepare grill for medium-high heat; oil grate. Brush both sides of bread with 2 tablespoons oil total and grill, turning occasionally, until toasted and lightly charred, about 4 minutes. Transfer grilled bread to a plate.
Season sardines inside and out with salt and pepper (no need to oil them, as there is so much naturally in their skin). Grill, turning occasionally, until lightly charred and cooked through, 5–7 minutes.
Serve sardines with tomato and grilled bread drizzled with oil and topped with basil.
