Wash the radishes, red onion, and jalapeño under cold water. Slice thinly, about 1/8 inch.

Transfer the sliced vegetables into a blender or food processor. Pulse until finely chopped but not puréed.

In a stockpot, add the chopped vegetables, vinegar, sugar, garlic, salt, mustard seeds, celery seeds, and dill weed. Stir and bring to a gentle boil.

Reduce heat to medium-low, simmering for about 10-12 minutes until thickened and radishes are tender.

Remove from heat, cool for 5-10 minutes. Transfer to a clean, airtight jar.

Seal jar and refrigerate for at least 24 hours to allow flavors to develop.