Roast the fennel: Preheat the grill to high heat. Place the fennel wedges on a lined baking tray, drizzle with olive oil, and season with salt and pepper. Grill for 15-20 minutes until tender and caramelized. Set aside.
Cook the pasta: Cook the tagliatelle until al dente. Reserve ½ cup of pasta water, then drain.
Make the buttery crumbs: In a large skillet, melt the vegan butter and sauté the shallots until translucent. Add the lemon zest and panko breadcrumbs, then cook until golden and crispy. Season with salt and pepper, then set aside.
Make the sauce: In the same skillet, pour in the vegan cream and stir in the ground fennel. Warm over medium heat. Add the roasted fennel wedges, tearing them into smaller pieces as you go.
Bring it together: Add a splash of reserved pasta water to loosen the sauce to your preferred consistency. Add the cooked tagliatelle and toss until evenly coated.
Serve: Divide between bowls and top with the crispy lemon butter crumbs. Finish with lemon slices and a sprinkle of fennel fronds.