I learned from this one, but I don't follow it exactly anymore.
I add carrots to mine and I don't put the olives in. The olives give it an amazing flavor, but DH doesn't like them. I cook the carrots and potatoes in the tagine at the same time until the potatoes are soft, but still firm. Then I take the potatoes out (that's why I cut them big enough), and put the frozen peas in for about 15 minutes. Then I put the potatoes back in. I add a tiny bit more water until the potatoes are at least in some of the water, then just cook until the liquid is reduced just a little. It's supposed to have some liquid, but not be soupy. Cooks in morocco don't take the potatoes out then put them back in, but that's the only way I can do it without my potatoes turning to mush and without my peas still being too firm. If you cook them too long they will be part of your liquid.