Nevada is a very small town, so "decent" is relative.
The best option is the Thai Cabin & Grill. The owner's family is Thai and while he's not a trained chef, he is a good cook. It's the freshest Thai food -- almost everything is cooked from scratch when you order. They're open for dinner Wed-Sun, 4-9 pm. It's hard to find because it's behind his house in a housing development on the west edge of town. The Bing map on Facebook is way off. The Google map gets you in the neighborhood but is off a little. Take Austin/US-54 west to the edge of town; turn right/north onto 1375 Road. (I think there's a windmill at the corner) Follow it north through a couple of stop signs (1st is at Walnut; 2nd is at Noah). Just after the 2nd stop sign, turn left/west onto E Nighthawk Rd -- it's just around the corner and there's a big sign. They have a limited selection of beer & wine.
If you want to drive 20 miles to the west, to Fort Scott (KS), you can eat at Nate's Place at the Lyons' Twin Mansions. Open for breakfast/brunch/lunch from 9-2, Tues-Sun. They have great sandwiches on focaccia including a vegetarian option. The salads could be made without meat, as could the pastas. Some times the soup du jour is meatless. They have some egg dishes as well as trout and tilapia, if those are options. Their hummus is good, and their sweet hash of diced sweet potatoes & apples is to die for. They have a full bar. I recommend the bloody mary.