I would patch it with drywall. Use a large piece behind the lath. You may have to clear away a few inches of the plaster that oozed between the lath originally. Then secure the drywall with long drywall screws. Now you will need another piece to fill the hole itself since the first one is behind the lath. And you probably need two depending on the thickness of the lath and original plaster - also remember drywall comes in 1/2 to 5/8 sizes so pick what adds up to the right thickness. Then mesh tape and smooth over with mud.