Other than a sandwich, what else can I make with a big jar of Muffuletta spread- you know, the olives and cauliflower and peppers marinated?

If you like that and olives. You might want to buy some now. There's an olive shortage that's driving up prices.
I've actually found good quality olive oil and muffuletta mix at "Big lots".

I'd be tempted to add to a savory bread pudding.

I have also used it on a crostini with smear of goat cheese-olive salad-slice of prosciutto; I have added it to both potato salad and egg salad as flavor enhancers; I have spread it with the muffuletta meats and cheeses on a whole ciabatta bread and then cut in small squares to make mini appetizers; and finally add it to a mixture of cream cheese and Parmesan and make savory palmier

Mash an avocado on good break, add Muffuletta!

Your mix sounds like an Italian pickle called giardinara....so ideas include mixing it with more veg you'd find on an Italian table, like roasted red pepper, zucchini, tomato, olives, artichokes. Serve as an antipasto or as a side dish. Mix in some tuna, anchovy, hard-cooked egg, boiled potato for a salada Nicoise. Put on a platter of delI meats (another antipasto). garnish a bean salad or spread (like hummus).

Use it on a burger, or to top baked potatoes!

Might be good to top grilled or baked seafood with it?

This is more like a sandwich, but a friend of mine once served crostini with a smear of chevre then topped with an olive spread (tapenade, I think). It was delicious because the chevre cut the saltiness of the olives. This should work with the muffaletta spread.

How about added to simple roasted vegetables? Or to rice or couscous or mashed potatoes? You might need to chop it up a bit or to pulse it in the food processor a few times.

Stir some into marinara sauce, add to scrambled eggs or frittata, mix with cream cheese to make a dip, use as a condiment for baked chicken, use as a dressing for a bean salad - lots of options.