First, combine sour cream, fresh lemon juice, chopped basil, garlic powder, salt, and pepper in a small bowl. Mix everything thoroughly until smooth and creamy. Place the dressing in the refrigerator so the flavors blend while you prepare the salad.
Wash and dry all vegetables before chopping them. Slice the lettuce, spinach, and radicchio into thin strips for the perfect chopped texture. Cook the bacon until crisp, then crumble it into small pieces and chop the hard-boiled eggs.
Add lettuce, spinach, radicchio, red onion, green olives, mushrooms, hearts of palm, eggs, and bacon to a large bowl. Toss everything gently so the ingredients distribute evenly. This creates a balanced mixture with lots of textures.
Sprinkle the crumbled blue cheese over the salad mixture. Pour about half of the prepared lemon basil dressing over the salad and toss lightly. Add more dressing if needed until the ingredients are coated but not soggy.
Divide the salad onto serving plates or bowls. Top each portion with crispy fried onions and halved cherry tomatoes. Serve immediately while the salad is fresh and crunchy.