Thinly slice the red onion and place it in a bowl. In a separate saucepan, combine vinegar and sugar, then heat until the sugar dissolves. Pour the mixture over the onions and let them sit for at least 30 minutes.

Prepare the Squash

Peel and dice the butternut squash into small cubes. Toss with olive oil, salt, and pepper. Roast in a preheated oven at 400°F (200°C) for about 25-30 minutes or until tender.

Make the Pea Purée

In a saucepan, combine peas, coconut milk, and green curry paste. Bring to a simmer and cook for 5-7 minutes. Blend until smooth, adding water if necessary for desired consistency.

Cook the Halibut

Season the halibut fillets with salt and pepper. Heat a skillet over medium-high heat with olive oil. Cook the halibut for about 4-5 minutes per side, or until cooked through and flaky.

Plate the Dish

On each plate, spread a generous amount of the green curry pea purée, place the halibut on top, arrange roasted squash around it, and garnish with pickled red onions and fresh herbs.