Were you told what your blood test result was? Knowing how far into the pre-diabetic range would help with guidance a bit. It would be the HbA1c blood test result (42-27 is pre-diabetic).
If only in low figures then small tweaks to your diet may be enough.
Since the topic rambled a bit and I'm one of the culprits I'll summarise what info we have so far, and hopefully you can comment / ask further questions.
As others have said, the figure to watch is the back of pack info - Total carbs per 100g. You also need to remember to multiply this, eg 20g per 100g means 80g in total if the meal is 400g.
@sean123 suggested possibly using an air fryer.
If you have the worktop space for one they are good, they cook food faster and normally have a few different functions (eg bake, roast, grill, reheat, and air-dry).
@Lucyr suggested that if eating 2 main meals a day that 40g per ready meal would mean looking for meals with somewhere around 10g total carbs per 100 gram
Like Lucy I always kept veg in my freezer, and added it to a ready meal to make it more healthy.
@Lizajane10 suggested checking M&S ready meals and others have said they are good. Liza suggested checking carbs on items such as: meaty stews with dumplings, cauliflower cheese, or a pre-prepared meat sauce which just needs veg / salad with it
@everydayupsanddowns suggested a combination of pre-prepared meal parts which just need combining / finishing off at home.
I believe I'm right in saying that potatoes have less carbs than rice or pasta. Also small potatoes (new / baby ones) have less carbs than large/old potatoes. If bought mashed with carrot or swede then that potato mix should be lower carb than potato alone (check the 'per 100g' info to be certain).
It seems likely ready meals with potato may be lower carb than the rice / pasta ones. This would vary depending on the meal recipe.
I would definitely opt for frozen ready meals over the ones from the chilled cabinets. Chilled foods will almost certainly have more additives to extend shelf life.
A quick easy meal to do at home can be an omelette with meat, cheese, or some veg added, or served with a side salad. In addition to cauliflower cheese, broccoli cheese is often sold as a ready meal.
I often use my airfryer to roast a mix of veg with some chopped up chicken (I use swede and butternut squash as a potato substitute there).
Buying a bag of pre-prepared fresh veg to add to a meal is always an option. Ditto with salad bags.
If you only have one main meal a day then you could adjust the total carbs in that meal to allow for less carbs eaten over the rest of the day. So the total 40g in one meal isn't a hard and fast rule.