If you don't like a certain vegetable in your recipe you can choose a similar substitute. For example, bell pepper, asparagus, tomato, cucumber, zucchini, eggplant, kale, cabbage, broccoli, green beans, brussels sprouts, celery stalks and radishes can all replace each other.
If you do not like onions, feel free to exclude them. Another option is to substitute them with chives, green onions, leek, or celery.
Instead of avocado it you could use pesto, nut butter, hummus.
As for olives, you could substitute them with capers, sun-dried tomatoes or with nuts and seeds.
Pumpkin can be substituted with other starchy vegetables like potatoes, sweet potatoes, beetroot, parsnip.