Cut off pointed end of garlic; place garlic on a piece of aluminum foil. Fold foil to seal.
Bake at 375° for 1 hour; cool. Squeeze pulp from garlic cloves into a bowl, and mash with fork; set aside.
Stir together oil and sage in a small skillet, and cook over medium-low heat 2 to 3 minutes or until fragrant and crisp. Remove leaves, and drain on a paper towel; reserve oil.
Prepare gnocchi according to package directions, substituting chicken broth for water. Drain, reserving 1/4 cup broth. Add gnocchi and reserved oil to roasted garlic in bowl. Add reserved 1/4 cup chicken broth, chopped tomatoes, and pepper, tossing to coat. Sprinkle with cheese and sage leaves; serve immediately.