This mission is extremely tricky, given you have 5 endangered Magnifying Grasses, and you must produce at least 7500 sun.
The main gimmick of this level is the sun production. 7500 sun is required to be produced, which is a lot. I conveniently used a boosted Primal Sunflower from Zen Garden, but any other boosted sun producing plant (Sunflower, Twin Sunflower, Sun-shroom) could also work (I don't know, I didn't test these).
By the end of the mission, it is possible you still may not have enough sun, so continually delay the zombies with whatever means possible. (This was the case for me, so I had to continually block a Carthead Zombie with boosted Primal Wall-nuts while it was still out of range of my Bonk Choy)
Very few Plant Foods are given in this mission, so be wary what you use it/them on.
So as long as you keep planting boosted Primal Sunflowers (or the boosted sun production plant of your choice) and Gold Bloom, the objective should be reached.
Zombies in this level are extremely tough, but boosted Primal Wall-nuts offer a lot of resistance to them. (Level 6 Bonk Choys are also quite powerful)
Be wary of Zombie Bulls, as their Imps can be launched past your defenses. However, the Imps land just short of the Magnifying Grasses, which can take them out with ease.