Peel the potatoes and cut into 5cm chunks. Put in a small saucepan of cold salted water and bring to the boil. Reduce the heat to medium and cook for 12-15 mins until tender. Drain the potato and return to the pan. Cover to keep warm.
Step 2 — Prep vegetables
While the potato is cooking, thickly slice the capsicum. Cut the zucchini into 1cm-thick slices lengthwise. Put the capsicum and zucchini in a large bowl, drizzle with 2 tsp olive oil, season with salt and pepper and toss to coat.
Step 3 — Season fish
FISH OPTION Crush or finely chop the garlic. Combine the garlic, half the Italian seasoning* and 2 tsp olive oil in a large bowl and season with salt and pepper. Add the fish to the seasoning mixture and turn to coat.
Step 4 — Grill fish and veggies
Heat a chargrill pan over medium heat until hot. Cook the fish for 3½-4 mins each side until golden and cooked through (to test the fish, flake with a fork; if it comes apart easily, it's cooked). Remove from the pan. Increase the heat to medium-high, add the vegetables to the pan and cook for 3-4 mins each side until tender and charred. Remove from the pan.
Step 5 — Toast seeds
Meanwhile, put the pepitas and sunflower seeds in a cold small frypan over medium heat. Toast, tossing, for 3-4 mins until evenly golden. Remove from the pan.
Step 6 — Mash potato and serve
Mash the potato until smooth. Add 15g butter and 1 tbs milk, season with salt and pepper and stir until combined. Divide the mash, fish and vegetables among plates. Scatter with the seeds and serve with the pesto.