GROW: The Book
Empty spot between tomatoes and bell peppers, with basil, marigolds and nasturtium nearby. What should I plant here??
Greens maybe? They would get some extra shade from the tomatoes. That's what I did and it worked pretty well! Hope this helps!
There are a couple of books on companion planting. Roses Love Garlic. Carrots Love Tomatoes. Even if you don't want to plant carrots, I'm sure there would be other suggestions. Both books are available at Amazon but they are older books so a trip to your local used book store might bring results.
@annebeloncik I was thinking the same thing as @COWLOVINGIRL with the tomatoes and peppers the spot should have filtered shade which is perfect for greens.