Most Sun Oven cooking is done in a covered pot. This is to keep the moisture in the food from fogging up the glass door which lowers the temperature of the cooking chamber. But I’ve found that some faster cooking foods, such as vegetables, come out better if left uncovered. Even without a lid they tend to be done by the time the glass fogs up and since the steam isn’t trapped in the pot they come out a little crispier.
Today I put it to the test with two batches of asparagus and acorn squash. There wasn’t any noticeable difference between the covered squash and the uncovered, but the uncovered asparagus came out slightly browned and with a pleasant crunch to it and the covered batch did not.
Covered or uncovered, it’s a good idea to set a timer when solar cooking spring vegetables, unlike meats and stews that seem to get better the longer they cook in the Sun Oven, delicate greens can overcook and get soggy.