Finely chop garlic, sprinkle with a pinch of salt, then mash with the side of knife to a fine paste. Transfer to a medium bowl and whisk in vinegar and 2 tablespoons oil. Add tomatoes; season with salt and pepper and toss to coat. Let sit, tossing occasionally, at least 15 minutes.
Meanwhile, prepare grill for mediumhigh heat. Brush both sides of bread with remaining 4 tablespoons oil and grill until lightly charred, about 2 minutes per side.
Just before serving, toss herbs with tomato mixture. Spread ricotta on toast and top with tomato mixture; cut toast in half.
Do ahead: Tomato mixture (without herbs) can be made 12 hours ahead. Cover and chill.
