Relax. Don’t sue. There was no metal in your vegetables. I’ll bet it was mainly the carrots that got charred, right? Here’s what probably happened.
Frozen foods usually contain ice crystals. But as I pointed out earlier, solid ice doesn’t absorb microwaves nearly as well as liquid water does. The defrost setting on microwave ovens therefore doesn’t try to melt the ice directly, but operates in short, food-heating blasts, leaving time between blasts for the heat to distribute itself and melt the ice.
But you didn’t use the “defrost” setting, did you? (Or maybe your oven doesn’t have one.) You set the oven for a high, constant heating level, which raised localized portions of the food to extremely high temperatures without allowing enough time for the heat to dissipate throughout the bowl. So those localized spots got burned and charred.
Why the carrots and why the sparks? (You’ll love this.) The peas, corn, beans, and whatever all have rounded shapes, but the carrots are usually cut into cubes or oblongs with sharp edges. These thin edges dried out and charred faster than the rest of the vegetables.
Now a carbonized, sharp edge or point can act just like the tip of a lightning rod, which attracts electrical energy toward itself and thereby prevents it from striking anywhere else. (Techspeak: Electrically conducting sharp points develop highly concentrated electric field gradients around themselves.) The highly concentrated, carrot-attracted energy is what made the sparks.
I know this sounds a bit farfetched, but it’s quite logical. It has happened before. Next time, use the oven’s “defrost vegetables” or other low-power setting. Or else just add enough water to the bowl to cover the vegetables.
Honest, your oven isn’t possessed by the devil.