Could do both, or even all three. Peas climb, so they don't need the low down space and are nitrogen fixers, so don't need so much nutrients. Courgettes ramble around on the ground and peppers can take the space in between.
Certainly I would try that: if they don't do so well, or look too crowded, they can be thinned out later.
Thanks for your replies, I just wanted to make sure there wasn't anything in the tomato grow bag that might inhibit growth.
I've already got a dozen courgette in the ground & a greenhouse half full of chillies & peppers but my pea crop has so far been a complete failure, so I'd like to get SOME peas to eat sometime this year
Peas without question. My greenhouse early peas are just finishing, although sadly none made it to the kitchen (I scoffed them all in the garden. I always do) You’ve already got enough courgettes to feed an army, and though you might want some at the end of the season, you can plant them later. Chillies would be fine, but not as yummy as fresh peas.
Definitely keep an eye on the water, though. Maybe put it in one of those growbag trays so you can soak it.