If your blood sugar is too high, you need more insulin.
There’s lots of room for investigation and looking into details and strategies, but it can be helpful in dealing with big spikes to start with the basics: when you eat, you need to take enough insulin, and you need it soon enough for it to have time to work.
For this kind of salad it appears that you need significantly more insulin than you took. Maybe there are more carbs than you thought, or maybe your insulin to carb ratio is off, or maybe you had some extra insulin resistance because of something else going on. Maybe pre-bolusing earlier would help. But you shouldn’t have to go to 400 or even 250 when you eat a salad, so it’s something worth working on and we’d all be happy to talk about it more. And if you are getting spikes to the 300s and 400s when eating, a good CDE or endo who is expert in diabetes could also be a helpful resource.