Tayari comes from طيار arab. which means "ready, done, prepared". The causative form is tayari- +-isha means "to prepare". A synonyme is kufanya tayari. So this is an arab expression. The Bantu expression is ku-andaa. They are synonyms
Are there any differences between them? For instance in english we usually say make food instead of prepare food, but either is acceptable. Make is less formal and indicates a lower level of effort