What is something simple (other than salt) that I add to plain chicken, pasta, and olive oil to make it tastier?

I make chicken with salt and pepper all the time. It's all you need. But other options include
- lemon, olive oil and oregano combination.
-balsamic vinegar
-smoked paprika
-harissa
-soy sauce , ginger and garlic

All of these suggestions are great, and I'll add another simple one: aglio e olio, which sounds fancy because it's Italian for "garlic and oil", but that's really all it is. It's about as simple and dressed down as a meal can be, yet always satisfying. Serious eats has a good tutorial on how to make it: https://www.seriouseats.com/recipes/2016/02/spaghetti-aglio-olio-recipe.html
Cook your chicken however you like (which again can be as simple as a pan fry), make the pasta, top it with chicken. The past sauce will still be tasty if you decide to top off your servings with a squeeze of lemon juice and a grating of parmesan, and if you have parsley it's a good garnish in this too.

Lemon peel and juice.

This time of year a favorite of mine is a simple chiffonade of fresh basil leaves with garlic quickly sautéed in olive oil. Sometimes I add balsamic vinegar, cherry tomatoes & mozzarella pearls.

You can add almost any fresh or dried herb here: thyme, rosemary, tarragon, even fresh chopped parsley will elevate and add a lot of freshness to this dish.

Additionally, you can try tossing in something like broccoli florets, or even some halved green or black or Kalamata olives or a few capers. If you like pesto, stir in a spoonful or two of that and it will add a great deal of flavor as well as the anti-oxidant properties of its ingredients.

Any of those would be great, especially Parmesan, which will add a lot of flavor. Garlic is the other thing that will help round out the dish - use as much or as little as you like (I like a lot). Lemon pepper is fine but a little squirt of fresh lemon juice could be even better! You can do endless variations on your ingredients but your ideas plus the ones I mentioned would give it plenty of flavor.