Preheat the oven broiler. Place the baguette slices on a baking sheet and place in the oven. Lightly toast both sides of the bread.
Mix together the pesto and tomato paste and spread a little on top of each toast, covering the surface completely.
Slice the tomatoes lengthwise, discarding a slim slice from the curved edges, to give 4 flat slices from each tomato. Lay a slice of tomato on top of each toast.
Place 1 small slice of cheese on each tomato slice, and drizzle with a little olive oil. Scatter with a few pine nuts and thyme or oregano leaves.
Place the toasts back under the broiler and broil until the cheese is beginning to melt and the pine nuts are golden, about 4 to 5 minutes. Serve the toasts hot, garnished with sprigs of thyme or oregano.