In a large pan over medium-high heat, heat oil. Season prawns all over with salt and pepper. When oil is shimmering but not smoking, add prawns and sear until underside is golden, about 2 minutes, then flip until opaque. Remove from pan and set aside.
Reduce heat to medium and add butter. When butter has melted, stir in garlic and cook until fragrant, about 1 minute. Add cherry tomatoes and season with salt and pepper. Cook until tomatoes are beginning to burst then add spinach and cook until spinach is beginning to wilt.
Stir in double cream, Parmesan and basil and bring mixture to a simmer. Reduce heat to low and simmer until sauce is slightly reduced, about 3 minutes.
Return prawns to pan and stir to combine. Cook until prawns are heated through, garnish with more basil and squeeze lemon on top before serving.