How you wound up with the leftovers: A recipe called for a tablespoon, but you opened a whole 6-ounce can.
Use it now: Take advantage of paste's concentrated flavor and make a tomato sauce in half the time it would take with whole or chopped tomatoes: Sauté a clove of garlic in olive oil, add paste (this works best if you have most of the can left over) and a cup of water, and season with salt, pepper and a dash of oregano. Bring to a boil and then let simmer for 15 minutes.
Use it later: Dole out tablespoons of paste onto a metal baking sheet and freeze. Once the lumps are completely frozen, store them in an airtight bag for up to six months.