Heat olive oil in large non-stick frying pan over high heat. Add garlic, fennel seed and chili flakes. Stir. Let cook about 1 minute until garlic just begins to brown. Add prawns and continue to cook, stirring occasionally until prawns just turn pink, about 2-3 minutes. Add the sliced fennel bulb, grapes and salt and continue to cook for 2 more minutes. Add white wine or vermouth and simmer briefly only about 30 seconds. Add butter and swirl pan to incorporate. Adjust seasoning to taste; sprinkle with fennel grass and serve.