Our family (2 Adults and 2 Picky eating boys) had an enjoyable dinner at the Abyssinia Cafe. They have a wide ranging menu and the service was good (Irish too!). Restaurant was not cheap - but nothing is in Mount Isa.
Also handy to a great lookout for a pre dinner stroll at sunset. You can see the lights of the mine slowly come on. Ask at the info centre for details of the lookout - it's not the touristy one!