Whisk together the mayo, Greek yogurt, vinegar, and salt until smooth. Mix in 2 tablespoons of pesto and taste. Add another tablespoon if you'd like a more assertive pesto flavor to shine through. The dressing should be thin enough to drip from a spoon. If necessary, add very small amounts of water, whisking after each addition, until the dressing is pourable. Taste, and add another pinch of salt to taste. Set aside. (Or refrigerate, if you're making the pasta salad later.)

Prepare the pasta according to package directions. Drain, and rinse well under cold water.

While the pasta cooks (and cools), prepare the remaining ingredients (see notes for tips on cooking bacon).

Set aside 1 strip of the bacon (store in the fridge); crumble the rest.

Pour about 1/2 cup of the dressing into a small container, and put in the fridge for later.

Add the crumbled bacon, tomatoes, onions, spinach, and avocado to a large bowl. Sprinkle a pinch of salt over the vegetables, then drizzle a little bit of the dressing. Toss to coat.

Add the pasta to the bowl, and gently fold all of the ingredients together to mix. Add the dressing in thirds, folding gently as you go.

Cover the pasta salad, and refrigerate for at least an hour, to let all of the flavors meld.

Thin the reserved dressing with a small amount of cold water or extra virgin olive oil (your choice). Drizzle the dressing over the pasta and fold gently. (The pasta will have absorbed a lot of dressing during its time in the refrigerator, so, the extra dressing will loosen things up and recoat the salad.)

Crumble the reserved bacon strip over the salad. Top with the crushed croutons and basil, and serve!