1. Whisk together ingredients for the honey mustard dressing and set aside.
2. Bring a large pot of salted water to a boil and cook pasta according to package instructions until al dente. Drain, drizzle with olive oil, and let cool at room temperature.
3. Meanwhile, preheat grill to medium-high heat.
4. In a large mixing bowl, toss together courgette and bell pepper with paprika, garlic powder, a drizzle of oil, salt & pepper.
5. Drizzle oil separately onto red onion and halloumi slices, and season with salt & pepper.
6. Grill vegetables until lightly charred but still crisp, 3-4 minutes per side. Wrap cooked red onions cover until ready to serve. Grill halloumi for 3-4 minutes per side.
7. Cool vegetables and halloumi slightly and cut into bite-sized pieces.
8. In a large serving bowl, toss together pasta, vegetables, halloumi and sun-dried tomatoes with the honey mustard dressing. Toss in tuna if using. Finish with basil and more salt & pepper.