Wash courgette and cut in thin slices.Peel and cut onions in quarters, then slice very thin. Add to courgette. Cover courgette and onions with 1 inch water and add salt. Let stand 2 hours. Drain thoroughly.
Bring remaining ingredients to boiling. Pour over courgette and onions. Let stand 2 hours. Bring all ingredients to boiling point and heat 5 minutes.
Pack hot into hot jars, leaving 1/4 inch head space. Remove air bubbles.