On a cutting board, using the flat side of a chef's knife, mash the garlic clove to a paste with a pinch of salt; transfer to a large bowl. Add the tomatoes, onion, vinegar and the 3/4 cup of olive oil and season with salt and pepper. Let the mixture stand at room temperature, stirring a few times, for at least 1 hour or up to 2 hours.
Light a grill. Brush the bread with olive oil and grill over high heat until toasted and lightly charred in spots, 1 minute per side. Let cool slightly, then cut into 1/2-inch cubes.
Add the bread and arugula to the tomatoes along with the ricotta salata and toss to combine. Serve right away.
Fresh summer tomatoes and ripe, fruity American rosés are a natural pairing, thanks to the similar brightness of their flavors.