Okay I know people get annoyed when you change up a recipe too much, but this came out really spectacularly so I thought I'd share.
I used half an onion rather than whole, and sauteed the onions and olives in about 3 or 4 Tbsp olive oil on medium heat until onions were mellow and brown. Added a basil leaf and some chopped fresh lemon thyme because I had some from the farmers' market and have no idea what to do with it. I also added about a teaspoon of dried oregano. I added three cloves smashed garlic, the chopped tomato, one can artichoke hearts, chopped, capers and about 2 Tbsp tomato paste - again because I had some sitting in the fridge. Covered the whole deal and simmered on the stovetop, stirring occasionally for about 10 minutes more.
I greased a pyrex pan generously with olive oil, placed the halibut in, rubbed with salt and pepper and poured the lemon juice directly on the fish, and then poured the pan sautee mixture over everything, and baked until done.
Served over sauteed spinach with a side of rice. Yum.