Cook pasta according to package directions; drain.
Meanwhile, heat 1 tbsp oil in large skillet set over medium-high heat; cook pancetta for 3 to 5 minutes or until golden brown and crispy around edges. Transfer with slotted spoon to paper towel–lined plate.
Season tuna with salt and 1/2 tsp pepper. In same skillet, cook tuna, turning once, for about 6 minutes or until golden brown on both sides. Transfer to plate. Let stand for 5 minutes, then slice.
In same skillet, cook cauliflower, shallots and garlic over medium heat for about 5 minutes or until slightly softened. Stir in wine; bring to boil. Cook for 3 to 5 minutes or until liquid is reduced by half. Stir in cream. Reduce heat to low; bring to simmer.
Add pasta to skillet; cook, tossing gently with sauce for 2 minutes. Remove from heat; add Parmesan, butter and parsley, tossing to coat. Stir in tuna.
Divide among plates. Scatter pancetta over top; sprinkle with remaining pepper.