1. In a 2 1/2- to 3-quart pan over medium-high heat, stir pancetta in olive oil until crisp and beginning to brown, about 5 minutes. With a slotted spoon, transfer half the pancetta to paper towels to drain.
2. Add chopped sage to pan and stir until fragrant, about 30 seconds. Add 5 cups water and bring to a boil.
3. Following steps 2 and 3 of basic polenta recipe, add polenta (omit salt in step 2) and cook until tender to bite. Add salt and fresh-ground pepper to taste (omit butter).
4. Ladle polenta into bowls and top with reserved pancetta.