First, cut yourself some slack! Going back to work is tough. Both my husband & I work 50+ hour weeks, so we also opt for 2 nights a week when we do shortcuts - one night we order pizza & salad. Another night we do a boxed or frozen meal. Keep in mind - not all frozen food is created equal. I'm really impressed when I read the ingredient list on the foods at Trader Joes. On their frozen food, every ingredient is something you can recognize, and not too high in fat or salt. We like their risotto, the indian food, the thai food, and some of the simple pre-cooked pasta packages. Sometimes, I'll steam some veggies in the microwave and add them in, or do a simple salad (greens, tomato, cucumber) on the side. We also sometimes short cut by having breakfast for dinner one night a week. Example, pancakes, scrambled eggs, omelets, fruit.
For other well-planned, cooked meals, I find that we end up using the same base ingredients and vary the starch, herbs, and cheeses to make it a new meal. Example: chicken, bell peppers & tomatoes is greek if you use oregano, lemon and feta. But it's mexican if you add cilantro, cumin, jack cheese and tortillas. The same basic incredients are perfect italian if you add some pesto & parmesan. Add some ginger, rice and it's asian stirfry. Try to do all the prep at the beginning of the week, and just assemble & add your herbs and cheese to make it feel fresh. For example, I'll grill a value pack of chicken breasts or steaks on Sunday. They can just be chopped up & added to pastas or tacos, salads or sandwiches during the week in 30 seconds. I'll also add some mediterranean veggies to the grill (bell peppers, zucchinis, eggplant, red onions), and they can also be thrown into pasta, salads, omelets, quesadillas, etc.
If I don't get all this mass grilling done on Sunday, I'll also plan ahead for reusing left overs. Example, I'll boil & shred some chicken for tacos one night, and plan to make tortilla soup the next night. Or I'll make a huge thing of pasta sauce with ground beef one night, and assemble a lasagne with the left overs before going to bed. I just throw it in the oven as soon as I get home at 6:15, and by 7, it's done.