I am invariably cooking with a toddler on my hip and now I have a mini electric chopper, (bit like this but mine was from Lidl) life is much faster. Just quarter and onion and shove it in and press and it's all finely chopped up in about 2 secs. Can also stick in peeled garlic gloves/root ginger with the onion if you need those in the base of your meal.
I use it to chop up (or if I go far enough, to puree) DD's food once cooked, to turn tinned plum toms smooth, to make pesto, to dice veg for soups (carrots etc), to chop nuts finely. It is bloody marvellous.
I also chop and freeze lots of ingredients on trays and then stick them in tubs so I can go to the freezer and grab a handful of chopped raw bacon bits and fling them in my pan (cook from frozen, shove in with the onions), a handful of diced peppers, a handful of chickpeas/cannelini beans/whatever other pulses! Frozen peas, broad beans, sweetcorn, spinach are all great.
Learn what you can cook from frozen to save on forethought. I find most fish is fine, I just sit the mackerel/trout/salmon etc fillet skin side down ontop of the veg I am sauteing to keep it slightly off the heat and it will be cooked by the time the veg is. Or stick it straight from the freezer into a pan of stock or milk if poaching.
Embrace the food processor (if you have a dishwasher!). Use it to grate whole blocks of cheese at a time and keep them in a tub in the fridge so it's easy to sprinkle a handful into a sauce/onto a dish going in the oven. Use it to slice up potatoes/veg for gratins/dauphinoise. Use it to slice fruit for crumbles. Use it to make pastry, to mix up crumble topping.
Get pans heating whilst you get your stuff chopped - soooo much quicker. And always preheat the oven whilst doing any hob based stuff and make sure your oven trays/dishes are in there so they are hot when you need them.
As you see I have had to embrace one handed cooking!! I now flit round the kitchen like a mad crazy thing but I did once get an apple and blackberry crumble prepped from scratch to in the oven in 7 mins, and that included stewing the fruit for a couple of mins so it was hot when it went in the oven