Instructions
Step 1
Make the pickled onions: In a small bowl, stir together the onion, bay leaf, habanero, sugar, and salt. Transfer to an 8-ounce jar, then add the vinegar, cover tightly with a lid, and shake well. (The pickling liquid may not cover the onion mixture at first, but the onions will wilt over time and end up immersed.) Refrigerate for at least 4 hours or up to 1 week, shaking occasionally.
Step 2
Make the lime salt: In a spice grinder or small food processor, pulse the salt and lime zest until well combined. Transfer to an airtight container and set aside. (The lime salt can be stored at room temperature for up to 3 months.)
Step 3
Make the salad: Fill a medium bowl with ice water and stir in the salt until dissolved. Add the radishes and set aside until very crisp, about 5 minutes.
Step 4
Drain the radishes through a fine-mesh strainer, discarding the soaking liquid, then return the radishes to the bowl. Drain the onions through the strainer, discarding the pickling liquid and the bay leaf, then add them to the bowl with the radishes. Add the watermelon, season to taste with black pepper, and gently toss with your hands until well combined.
Step 5
Transfer to a platter and top with the mint and a drizzle of oil. Sprinkle with lime salt to taste just before serving.