Heat 1 ½ t olive oil in a large nonstick skillet over medium-high heat. Add onion to pan, and sauté for 3 minutes, stirring frequently. Clear a spot in bottom of pan. Add garlic to clear spot in pan, and sauté for 30 seconds. Add salt, thyme, and pepper; sauté 30 seconds, stirring frequently. Add reserved morel mushrooms and cremini mushrooms to pan. Cover, reduce heat, and cook for 4 minutes. Uncover, increase heat to medium-high, and cook 2 minutes or until liquid almost evaporates, stirring frequently. Clear a spot in bottom of pan. Add tomato paste to clear spot; cook 1 minute. Stir tomato paste into mushroom mixture.