Also, if it's too warm for peas to fruit, then it's much too hot for broccoli which is happiest when it's in the 30's over night and in the 40's and 50's in the day. Warm temps cause broccoli to go to seed quickly. Broccoli is a pretty heavy feeder, so a newly prepared sheet mulch bed may not yet be fertile enough for it. If it were me, I'd be putting aerobic
compost tea on that sheet mulch every few days to help it decompose. I'm even wondering if that really is a broccoli plant. Could it be an imposter like brussels sprouts? Spinach does not like a lot of fertility, so the fact that they look great tells me that the sheet mulch hasn't decomposed too much yet.