Preheat the grill to medium-high.

With a pastry brush, lightly coat both sides of the bread with the extra-virgin olive oil.

Place the tomatoes on the grill and roast, turning, until the skin is evenly charred. Remove the tomatoes. Place the bread on the grill and cook, turning, until marked and lightly toasted on both sides, about 2 minutes. Remove from the grill and set aside.

When cool enough to handle, peel and seed the tomatoes.

Place the tomatoes in a blender with the oil, vinegar, and garlic and blend until smooth. Season with salt and pepper, to taste.

Place the spinach in a large salad bowl and top with the artichoke hearts and onions. Toss with the dressing to lightly coat. Crumble the blue cheese on top and serve with the toasted bread on the side.