For the onions:
2 cups (480mL) cider vinegar
1/4 cup (60mL) unrefined cane sugar
1 1/2 teaspoons (8mL) fine sea salt
1 red onion, thinly sliced

For the asparagus:
1 pound (454g/16oz) asparagus, ends trimmed
2 tablespoons (30mL) mild extra-virgin olive oil
Sea or Himalayan salt to taste
Freshly ground pepper to taste

Put the cider vinegar, sugar, and salt in a glass bowl. Whisk until the sugar and salt has dissolved. Add the red onion, making sure it is completely covered. Cover and refrigerate for 24 hours.

Before serving, preheat the oven to 425 degrees F. Toss the asparagus with the olive oil, and place on a baking sheet in a single layer. Sprinkle with salt and pepper. Roast for 12 to 15 minutes, shaking the pan mid-way, until tender crisp and browned. Serve warm with the pickled onions.