Macerate the Onion: In a small bowl, combine the sliced onion with 1 tablespoon of red wine vinegar. Let it sit for 20 minutes to soften and lightly pickle the onions.
Prepare the Croutons: While the onions are macerating, preheat the oven to 400°F/200°C (180°C fan-assisted). Line a baking sheet with parchment paper. Spread the bread pieces on the sheet, drizzle with olive oil, toss, and sprinkle with coarse sea salt. Bake for 5-6 minutes until crisp and golden. Monitor closely to prevent burning. Remove from the oven and set aside to cool. If the bread is not crisp enough, it may need 2-3 more minutes.
Blanch the Asparagus: Heat a large skillet over medium-high heat. Add water to a depth of about 2,5 cm and bring to a simmer. Add the asparagus and cover, allowing it to steam for about 3 minutes, until just tender but still slightly crunchy in the center. Immediately remove the asparagus from the skillet and rinse under cold water to halt the cooking process.
Assemble the Salad: In a large salad bowl, combine the blanched asparagus, macerated onions (without the vinegar), sliced strawberries, and chopped mint. Toss gently.
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