For garlic breadcrumbs, heat olive oil in a frying pan over medium-high heat, add breadcrumbs and garlic and stir continuously over medium-high heat until golden (4-5 minutes). Season to taste, cool, stir in parsley and reserved fennel fronds and set aside.
Heat olive oil in a large saucepan over medium-high heat, add onion, fennel and garlic, stir occasionally until tender (4-5 minutes). Add pancetta, cook until crisp (2-3 minutes), then add vongole and wine. Cover with a lid and cook, shaking pan occasionally, until vongole open (2-3 minutes). Season to taste, scatter with garlic breadcrumbs and serve immediately.