Rinse and halve the peppers. Remove the seeds, and cut into thick strips lengthwise. Rinse the lemon in hot water, then thinly slice. Peel and halve the onions. Blanch the onions and peppers in boiling salted water for 3-4 minutes, then remove and drain well. Divide the onions, peppers, rosemary leaves, and lemon slices into the prepared jars. Bring the vinegar, 200 ml (approximately 7 ounces), oil, salt, peppercorns, and sugar to a boil. Pour over the vegetables, until they're all covered, and seal tightly.
Cool completely in a dark, cool place. Let infuse for 1 week before using.