You are in the right place for Takeaways! Not quite as good as London but I think it comes close.
I'll try list some below in categories!
Burgers and Wraps Shake n Grill - they do meal deals and really really good milkshakes. Umami - Burgers, wraps and peri chicken. So good! 7 Bone - restaurant but they also deliver via Deliveroo Jags 119 - american diner style food Burgers and brews or Bangers and brews - same chain one is for burgers and one is for hotdogs!
Pizza Greenwich brew pub - amazing pizzas, in the restaurant you can get huge 20inch pizzas, but you can get smaller ones delivered! Circola - proper authentic style pizza Perfect Pizza company- cheap and cheerful. Roma Pizza Southsea village - 2 for one on Tuesdays in the pub.
Mediterranean Food Steki - deliver full Greek meals Gyros-land - Uber-eats in the summer Leilamezze
Indian Anwars Kadir Indian street food Spice fusion Purple Mango Akash
Mexican food Kick Ass Burrito Acapulco
Asian Thailand Cafe Bubble and pho Lins Thai Cafe Koh Thai Twins Chinese Hotpot restaurant Tangs Sakura - Japanese