More Fiber for 8 YO

Warning:poop mention

Can anyone help me think of ways to incorporate more fiber into our diets? I have an 8yo and a 10yo and I think my 8yo has a constipation issue. He only goes about once a week and when he does go ....... (TMI) it’s huge and very hard. Like the size of his leg...no exaggeration.....He does eat most vegetables that I prepare like broccoli, green beans and even brussel sprouts but I only know how to include those with dinner. I think we could all benefit from having a vegetable with at least both lunch and dinner.

Any recipes you may have, feel free to share!

SN: He refuses to try breakfast smoothies with fruits and veggies, I’ve tried many times.