Preheat oven to 300 degrees. Place large platter covered with towel in oven.
Heat oil to 370 F in a 6-inch tall frying pan with basket. Make batter by stirring together flour, semolina, baking powder and salt. Slowly add cold water, stirring until smooth batter is formed. Add oil and stir through.
To cook, dip vegetables in order of ingredients in as little batter as possible and fry until each is golden brown and crisp. Drain after frying on paper towels. When drained, arrange on platter. Move quickly -- each vegetable should take 3 to 4 minutes at most. When finished with zucchini blossoms, sprinkle whole platter with kosher salt and serve immediately with lemon wedges.