In a medium-sized pot, heat up the oil and sauté the onion until soft and translucent.
Add the strawberries, garlic, vinegar, sugar, pepper and mustard seeds. Bring to a gentle simmer, cover and leave for 25-30 minutes, stirring occasionally, until thickened.
Take off the heat and add the lime juice. Adjust the seasoning and pour into sterilised glass jars.