Agree that Nigella's chocolate olive oil cake is v. good. Great with raspberries, as she recommends. Or you could make raspberry coulis to pour over (just mashed up raspberries with icing sugar and perhaps just a little gin...)
To 'compete' with the chilli (if you wanted) you could make a Mediterranean-style bean dish:
red peppers, courgettes, aubergines, red onions, garlic, sweet paprika, oregano all sliced then gently frizzled in olive oil. When softened/just beginning to brown, slowly simmered with a tin of plum tomatoes in juice, a tin of butter beans (or other beans of your choice), drained, atablespoon tomato puree, just a little water (or vegan red wine), plus salt and pepper to taste. Just before serving, top with lots of fresh basil. Great served hot with rice and tenderstem broccoli .
For a buffet:
Does he eat fish? If so, hot-smoked salmon or trout or gravadlax, or nicely poached cold salmon, or salmon pate or kipper pate (easy to make at home using vegan soft cheese/yoghurt/mayo plus parsley and herbs). Perhaps as a platter of 'salmon three ways' - hot smoked, cold poached, and pate or gravadlax. With sliced lemon and crisp lettuce/rocket.
Or cook usual the thin sliced smoked salmon in a frittata. Great with watercress or tiny sprigs of broccoli included.
Or a leek and asparagus frittata. Top with grated vegan cheese if liked.
Or mushroom frittata with some fresh spinach and tarragon and lots of black pepper.
Or Spanish slow-cooked tortilla with good olive oil, onions and potatoes.
Mini versions of all the above make nice buffet food.
Guacamole without the soured cream - I prefer it that way - and really nice posh gluten-free bread or crackers.
Mushroom pate (easy, using vegan soft cheese).
Home-made roasted red pepper hummus with nice veg crudites and marinated olives.
Good quality roast/smoked nuts (almonds etc). Or Nigella's Bar Nuts, if you replace the butter in her recipe with olive or other vegetable oil:
https://www.nigella.com/recipes/bar-nuts
Fancy rice salad - for example https://feelgoodfoodie.net/recipe/rice-salad/ or (more ambitious) https://nadiashealthykitchen.com/crispy-rice-salad/
There are lots of other possible salads here:
https://www.themediterraneandish.com/category/salads/
Also, what about Thai/Chinese etc dishes using tofu etc? There's a whole world of Asian dishes using vegetables, vegan protein and rice.